1. Field of the Invention
The present invention relates to a battery pack.
2. Description of the Related Art
A lithium secondary battery may be fabricated in the form of a battery pack. The battery pack may include a bare cell composed of an electrode assembly having a positive electrode plate, a negative electrode plate and a separator, a can for housing the electrode assembly, and a cap assembly for sealing an open upper part of the can. The battery pack may also include a circuit module having circuit elements such as charge/discharge devices and protection circuit devices connected to the bare cell; and an external cover connected to the bare cell and covering the circuit module.
The lithium secondary battery generally employs protection circuit devices such as positive temperature coefficient (PTC) devices, thermal fuses, and the like. These PTC devices and thermal fuses are typically secondary protection devices, separate from and in addition to the separator which is a primary protection device furnished in the bare cell. The secondary protection device is electrically connected to a charge/discharge circuit of the bare cell to thereby interrupt a flow of electrical current to the outside when the battery pack rises to a threshold temperature or when a disturbance of a preset voltage occurs due to excessive charge/discharge or the like. That is, the secondary protection device serves to prevent explosive rupture of the battery pack.
In a conventional battery pack, the circuit module is installed with the secondary protection device in conjunction with the inclusion of a lead plate for electrical connection between the secondary protection device and the bare cell, thereby requiring a space for mounting of the secondary protection device and the lead plate in the circuit module. As a consequence, there are limitations associated with the installation of numerous circuit elements in the circuit module. Therefore, the circuit module requires a circuit board having a multilayered circuit pattern therein, which disadvantageously leads to increased production costs of the battery pack.
Further, in a typical conventional battery pack, the secondary protection device is connected through the circuit module to the bare cell, which may result in low heat transfer efficiency from the bare cell to the secondary protection device. For this reason, the conventional secondary protection device suffers from deterioration of reliability for preventing the risk of battery pack rupture.